Summary of Significant Accounting Policies - Goodwill, Intangible Assets and Other Long-Lived Assets (Details)	12 Months Ended
	Dec. 31, 2018 reporting_unit
Property and Equipment [Line Items]
Number of reporting units	1
Minimum
Property and Equipment [Line Items]
Useful Life (in years)	4 years
Maximum
Property and Equipment [Line Items]
Useful Life (in years)	10 years